In the study of the Type II superstring, it is useful to consider the BRST complex associated to the sum of two pure spinors. The cohomology of this complex is an infinite-dimensional vector space. It is also a finite-dimensional algebra over the algebra of functions of a single pure spinor. In this paper we study the multiplicative structure.The central object of the pure spinor formalism is the BRST operator Q, which involves nonlinearly constrained ghosts. For example, the Type IIB superstring uses two ghosts λ L and λ R , which are spinors of so(10) satisfying the pure spinor constraint:Roughly speaking, the BRST structures are in one-to-one correspondence with SUGRA backgrounds. For a given background, the cohomology of Q describes its infinitesimal deformations. It was shown in [1,2] that the knowledge of the cohomology of the simplified differentialwhere θ is an odd spinor variable is useful for understanding the cohomology of Q. The cohomology groups of Q (0) were calculated in [2] as modules over the ring of polynomials of λ α L , λ α R . In the present paper we will study the multiplication of the cohomology classes, and calculate the cohomology as a ring. This allows us to simplify the description of cohomology. We can use the multiplication in cohomology to obtain information about cohomology of more complicated differentials.Let us consider the ring A = C[λ L , λ R , θ] of polynomials depending of ten-dimensional even pure spinors λ L , λ R and a ten-dimensional odd spinor θ. In other words, this means that the components λ L , λ R obey the pure spinor constraint (1) and the components θ α are free Grassmann variables. We define a differential acting on A by the formula: